A generic device is known from U.S. Pat. No. 3,547,512. Due to the slit-shaped diaphragms in the observation beam path and in the illumination beam path, only a small area of the fundus is illuminated and simultaneously observed. In order, nonetheless, to be able to examine a larger part of the fundus, the illumination diaphragm and the observation diaphragm are moved synchronously, whereby a part of the fundus is scanned. If the fundus is observed using a detector that demonstrates a certain inertia and the movement of the slit images of the diaphragms occurs repeatedly fast enough over the same part of the fundus the single images melt to a whole image of the scanned part of the fundus.
This device should, in particular, improve observing the eye through a cloudy respectively opaque eye lens by reducing generation and observation of stray light including the resulting glare. A real intermediate image of the retina is generated outside the eye by means of an ophthalmoscopic lens, with the illumination means and the magnifying optical system being focused onto the plane of this intermediate image.
However, satisfactory results cannot be obtained just by means of the previously described measures. U.S. Pat. No. 3,547,512 therefore utilizes additional diaphragms respectively mirrors which mask out half of the observation beam bundle respectively of the illumination beam bundle in such a manner that the observation beam bundle and the illumination beam bundle run separately with the exception of a small intersecting region of the plane of the object. Although the generated respectively observed stray light is successfully further decreased in this way, the light intensity and the obtainable resolution are greatly diminished due to the confines of the apertures of the observation beam bundle and of the illumination beam bundle.
WO 97/15855 describes another generic optical device which should permit contrast-free and glare-free examination of the fundus thereby making the finest details visible. With this device, too, the fundus is at least partially illuminated with an illumination beam and the light reflected at the fundus is imaged as an observation beam via an optical lens system into an intermediate focal plane from which the illumination beam is imaged via an eyepiece unit for further analysis. This prior art arrangement is designed for contrast enhancement in that light-intensive interfering parts of the radiation are selectively weakened in such a manner that light-weak interference phenomena are also detectable. However, an eyepiece optic is still required, because additional light beams cannot be coupled into the illumination beam path and the observation beam path without considerably interfering with the overall optical system.